The vehicle in this report is my primary commuter, and sees 90 to 120 moderate highway miles daily, with longer interstate trips from time to time. It never sees trips of less than 15 miles.

The oil filter in this interval was a Mann HU 726/2 X.

The 1/2-quart of make up oil was added about halfway through the interval, or about 7,000 miles before the sample was taken. Total sump capacity is 4.8 quarts.

For some historical context, the oil in the column dated 10-6-13 was T6 and in the 3-9-14 interval it was Amsoil HDD 5w-30. I notice an increase in some additive elements (Zn, P, Mg, allowing that the increased Ca may be carryover from the Ams HDD) between the T6 used in the 10-6-13 interval and this one. Did SOPUS fortify the add pack of T6 or is something else going on?

What's the consensus opinion on the lead level Blackstone flagged? How often do these trends resolve themselves (trend down) versus indicate a serious problem?

A lead reading of 8 is not by itself a concern. If it's a spike, it's not a very significant one. Watch how it trends in subsequent UOA's.

You should be able to extend the OCI's significantly judging by the TBN of 5.6 at 13k miles. RT6 starts with TBN of 10.6, and Blackstone recommends oil changes at 1.0, so there is still a lot of life left in that oil. Try extending the next OCI to 16k. I think it could even go much further than that.